In a strongly-worded speech to university chiefs he said there are "incentives" for institutions to hand out more top degree honours, such as league table rankings, but warned that grade inflation does not spur students on to work hard, or institutions to focus on offering high-quality teaching.

Research this summer found the proportion of firsts handed out by UK universities has soared, with one-third of institutions now grading at least one in four degrees with the top honour.

In some cases, the proportion has more than doubled in five years, according to the analysis of official data.

Mr Johnson told the Universities UK annual conference: "There has been a significant increase in the proportion of people receiving firsts and 2:1 degrees over the past five years that cannot be explained by rising levels of attainment.

"Grade inflation is ripping through English higher education."

The facts are "startling", the minister said, noting that figures published by the Higher Education Statistics Agency (HESA) showed that in the last five years alone, the proportion of students gaining a first class degree increased by more than 40%.

Almost one in four students now got the highest honour, up from 17% in 2011/12, he added.